import java.util.Scanner;

public class Zxf14 {
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        System.out.println("输入购买长度:米");
        int a=in.nextInt();
        if(a%3>0){
            System.out.println(a/3+1);
        }else{
            System.out.println(a/3);
        }
    }
}
